The overall objective of this project is to learn more about the mechanisms by which trisomy for human chromosome 21 interferes with normal development and function to result in the neurologic abnormalities commonly observed in Down syndrome. Over the past five years, we have constructed physical maps of human chromosome 21 which have been used in conjunction with patients who have imbalance for different portions of chromosome 21 to demonstrate that imbalance of a 10 megabase "critical region" of the long arm of chromosome 21 results in more severe neurologic abnormalities than imbalance of other segments of he chromosome. We now propose to develop a comprehensive approach for identifying genes encoded by this 10 megabase region of chromosome 21, and to determine which genes encoded by this region are most likely to result in neurologic abnormalities when present in three rather than two copies. Initially, we will focus our attention on the 2 Mb portion of the 10 Mb critical region of chromosome 21 that contains the EPM1 gene. This gene, when mutated, results in an autosomal recessive form of progressive myoclonous epilepsy. As part of a systematic analysis of chromosome 21 transcripts from this region, we propose to isolate the EPM1 gene by "positional cloning". Since mutation of EPM1 is known to result in adverse neurologic consequences. Thus, we particularly interested in isolating this gene, gaining insight into its function through sequence analysis, and studying its expression in trisomy 21 versus diploid cells. In addition to isolation and characterization of EPM1, we will study the transcriptional pattern in trisomy 21 versus normal diploid cells for each of the estimated 300 genes that we propose to isolate from the 10 Mb critical region of the chromosome. A primary goal of this proposal is to determine what fraction of chromosome 21 genes demonstrate dramatic increases or decreases in gene expression at the transcriptional level when present in genes through a comparison of their sequences with those of known genes.